The One With Rachel's Sister - S6-E13
Corrected entry: When Rachel comes in to spy on Ross through Monica and Chandler's window we hear the shower water running and both Monica and Chandler are in the bathroom. However, Chandler comes out wearing a T-shirt under his robe (and he's wearing socks). This seems to assume that he is dry (as the T-shirt is dry too). Also we can see that Monica is wearing her nightdress under her robe when we see down to her feet, so how could one or both of them have been showering?
Correction: It could have been bathwater running, and they were not yet in the tub.
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